10g RAC and GPFS

i am implementing 10gR2 RAC on GPFS 3.3 and AIX 5.3 ML4. i had a question concerning asynch i/o and filesystem i/o with gpfs. i know GPFS uses direct i/o. so how should i handle the parameters? i have DISK_ASYNCH_IO set to TRUE and FILESYSTEMIO_OPTIONS set to asynch. i know that FILESYSTEMIO_OPTIONS should probably be set to SETALL. is it best to simulate asynch io using multiple db_writers (and setting DISK_AYNCH_IO to FALSE)?

any advice on these parameters with GPFS would be greatly appreciated....